Atrial flutter is an electrocardiographic descriptor used both specifically and nonspecifically to describe various atrial tachycardias. The term was originally applied to adults with regular atrial depolarizations at a rate of 260-340 beats per minute (bpm). Historically, the diagnosis of atrial flutter was restricted to those patients whose surface electrocardiogram (ECG) revealed the classic appearance of "flutter waves." This sharp demarcation is used less frequently in the current era, where the more electrophysiologically descriptive "atrial reentry tachycardia" is used instead.
Atrial flutter is infrequent in children without congenital heart disease. In these patients with otherwise normal cardiac anatomy atrial reentry tachycardias are observed mostly during fetal life in late pregnancy, and during adolescence.
In the fetus, atrial flutter is defined as a rapid regular atrial rate of 300-600 bpm accompanied by variable degrees of atrioventricular (AV) conduction block, resulting in slower ventricular rates.
During this type of tachycardia, the atrial rate is so rapid that normal AV nodes usually display a physiologic second-degree block, with a resultant 2:1 conduction ratio. In individuals with AV nodal disease or increased vagal tone, or when certain drugs are used, higher degrees of AV block may develop, such as 3:1 or higher. In individuals with accessory AV nodal pathways, a 1:1 conduction ratio may occur through the accessory pathway with resultant ventricular rates of 260-340 bpm, which can cause sudden death. A 1:1 conduction ratio may also occur when the atrial rate is relatively slow (eg, < 340 bpm) during atrial flutter or when physiologic processes facilitate AV nodal conduction, such that a rapid ventricular response can still result in sudden death.
Patients who have undergone Mustard, Senning, or Fontan operations are more prone to developing this arrhythmia because of atrial scars from surgery and right atrial enlargement, such as after the classic Fontan operation. Similarly, patients who have undergone surgical repair of an atrial septal defect, total anomalous pulmonary venous connection, and tetralogy of Fallot may later develop atrial flutter.  Individuals with muscular dystrophies such as Emery-Dreifuss  and myotonic dystrophy  may also develop atrial flutter, as well as those with dilated, restrictive, andhypertrophic cardiomyopathies.
Treatment of children with atrial flutter depends on the age of presentation and baseline cardiac anatomy. Fetal atrial flutter is usually treated with oral maternal antiarrhythmics without need for further intervention if ventricular function is acceptable and if there is no placental edema. Once the baby is born, it usually responds well to oral antiarrhythmics until it resolves. In the other age groups and in patients with baseline abnormal cardiac anatomy or surgical scars, it usually recurs. In general, treatment may involve medication, cardiac pacing, cardioversion, radiofrequency catheter ablation, or surgical procedures (see Treatment). Drug therapy of atrial flutter in children can be classified under the 3 broad headings of ventricular rate control, acute conversion, and chronic suppression (see Medication).
Atrial flutter is a reentrant arrhythmia circuit confined to the atrial chambers. As a rule, atrial flutter originates in the right atrium, whereas atrial fibrillation, which is more frequent in adults, originates in the left atrium.
A flutter circuit typically surrounds an anatomical or functional barrier and includes a zone of slow conduction (or conduction over an extended circuit) and an area of unidirectional block, as required for reentry of all types. Frequently, a premature beat blocks one limb of the circuit and is sufficiently delayed in the other limb (while traversing around the anatomical or functional barrier) to allow for recovery from refractoriness in the first limb.
The reentrant circuits that occur in children with atrial flutter after congenital heart disease surgery are believed to involve abnormal atrial tissue that has been subject to chronic cyanosis, inflammation secondary to surgery, scarring, and increased wall stress in cases of enlarged atria. Such circuits may encircle anatomical barriers such as atriotomy scars or surgical anastomoses, and they may use areas of slow conduction along baffle limbs and other sites of injury in addition to the tricuspid valve–coronary sinus isthmus.
Sinus node dysfunction with bradycardia is generally present in many of these patients years after surgery. This is a contributing factor for development and maintenance of atrial flutter.
Atrial flutter circuits in children with congenital heart disease are typically more variable than those in adults. For the most part, atrial flutter circuits in adults are confined to the tricuspid valve–coronary sinus isthmus (or isthmus-dependent flutter).
In the fetus, atrial flutter occurs mainly during the third trimester. The atrium is believed to reach a critical mass to support an intra-atrial macroreentry circuit at about 27-30 weeks’ gestation.
Most fetuses and neonates with atrial flutter have structurally normal hearts. However, when atrial flutter is detected in a fetus, structural cardiac anomalies such as Ebstein anomaly of the tricuspid valve and AV septal defects should be ruled out because of a higher incidence of such defects in these cases.
Some newborns and young children have associated conditions or anomalies that may predispose them to atrial flutter. Atrial septal aneurysms appear to be associated with sustained atrial arrhythmias in newborns. Restrictive cardiomyopathies are also associated with refractory atrial flutter. In Costello syndrome, the dysmorphic appearance is also associated with a dysrhythmia characterized as chaotic atrial tachycardia, and this dysrhythmia may include long episodes of atrial flutter.
Atrial flutter is not uncommon in the immediate postoperative period after congenital heart surgery. Surgery-induced inflammation of the pericardium, scarring, and volume overload may trigger atrial flutter.
Case reports have linked atrial flutter to ingestion of herbal medicines and certain foods. These episodes did not recur after avoidance of the triggers.
Atrial flutter and atrial fibrillation have been related to obesity, alcohol consumption, and hyperthyroidism. [4, 5, 6] One study reported that in adults, diabetes mellitus is a strong independent risk factor for development of atrial flutter and atrial fibrillation. 
Atrial flutter is most commonly seen after the Senning or Mustard surgical procedures for transposition of the great arteries and after Fontan repair. According to one United States study, 57% of patients with double-inlet left ventricle who undergo the Fontan operation may be expected to present with atrial flutter or fibrillation by 20 years after surgery.  The mean annual incidence of new dysrhythmias (predominantly atrial flutter) after the Fontan operation is 5%. According to a multicenter study, tachyarrhythmia prevalence over time was similar between the intracardiac lateral tunnel and the extracardiac conduit Fontan operations. 
In one international review, atrial flutter accounted for 26.2% of all cases of fetal tachyarrhythmias, and supraventricular tachycardia (SVT) accounted for 73.2%.  In an earlier population study of 3383 English newborns by Southall and colleagues, only 1 newborn had atrial flutter.  This likely underestimated the incidence of atrial flutter in utero because spontaneous conversion often occurs during birth and subsequent recurrence is uncommon.
A long-term follow-up study into adulthood of patients undergoing the Mustard or Senning procedure for correction of D-transposition of the great vessels demonstrated SVT in 48%, of which atrial flutter was the most common type (73%). Arrhythmias accounted for 12.7% of pediatric cardiology consultations in a major pediatric academic medical center, of which atrial flutter was the second most common type.
Sexual and age-related differences in incidence
Following atrial septal defect repair, the prevalence of atrial flutter is higher in females (70.7%) than in males. Patients with Fontan repairs present with flutter either as children or as adults. Patients with repaired tetralogy of Fallot tend to present with atrial flutter as young adults. Because the Mustard and Senning procedures are now rarely performed, the cohort of patients with this substrate typically consists of older adolescents and adults.
One study reported that the recurrence rate of atrial flutter and fibrillation in women with preexisting cardiac rhythm disorders during pregnancy was the highest of all the studied arrhythmias, reaching 52%. 
Neonatal atrial flutter is usually a self-limiting illness, requiring only conversion of the rhythm with esophageal atrial pacing or cardioversion. Incisional reentrant atrial tachycardia following complex atrial surgery in the repair of congenital heart disease may occur early in the postoperative period; this event is predictive of the occurrence of late postoperative flutter. The prevalence of atrial flutter in several classes of postoperative patients increases with the duration of follow-up care.
Morbidity and mortality in patients with atrial flutter largely depend on the following factors:
Age at presentation
Cardiac anatomy (normal anatomy vs congenital heart disease)
Integrity and anatomy of the myocardial conduction system (normal sinus node vs sinus node dysfunction; AV block vs normal AV node, with or without accessory pathways)
Prompt recognition of the arrhythmia and initiation of adequate therapy
The fetus with atrial flutter may have significant morbidity and be at risk for mortality. According to one review, hydrops fetalis developed in as many as 40% of fetuses with atrial flutter. The mortality rate in these fetuses was 8%. 
Mortality in newborns with atrial flutter is uncommon. Most patients remain in sinus rhythm following their initial conversion, and the need for antiarrhythmic prophylaxis in these patients during infancy is debated.
In patients with postoperative atrial flutter that develops late following repair of congenital heart disease, the severity of presentation depends on the atrial flutter rate, conduction ratio, and presence of ventricular dysfunction. In patients who have undergone the Mustard procedure, Holter recordings incidentally capturing episodes of sudden fatality confirm that rapidly conducted atrial flutter is the dysrhythmia most frequently responsible for these fatalities.
In contrast, patients who have undergone the Fontan procedure rarely die suddenly but frequently present with symptomatic atrial flutter. This may be caused by a relatively slower atrial flutter rate, a higher degree of AV conduction block, or both.
Prolonged episodes of atrial flutter in asymptomatic or mildly symptomatic patients may be associated with development of atrial thrombi and although rarely in the congenital heart disease population, the possibility of thromboembolic events.
When women with heart disease and arrhythmias reach childbearing age, arrhythmias can recur during pregnancy. These arrhythmias significantly increase the risk for the mother and fetus.
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